Tuesday, March 6, 2012
Electric Pickup Truck Re-wire
A couple years ago, a class of undergraduate students at my college converted a 1997 Ford Ranger pickup truck to electric power. This vehicle originally sported a 4-cylinder gasoline engine with 5-speed manual transmission. It now has an electric motor and control system bought from Electric Vehicles of America. This company sells parts for conversion of cars, trucks, motorcycles, and even boats to electric power. You can find them at the following link:
A bank of 20 six-volt golf cart batteries supply 120 volts DC to run the motor. A separate 12 volt battery supplies power for lights, turn signals, and the control system that handles the motor. As it sits today, this truck has a range of 40 - 50 miles on a charge, and can reach 65 miles per hour. Granted, the range is limited. But it works fine for local driving and short commutes.
This vehicle was originally conceived as a test bed for experimenting with fuel cells and, possibly later on, hybrid power systems.
Having driven it myself I can attest to its quiet operation. At highway speed the motor emits a low hum - mostly what you hear is road noise off the tires.
Under The Hood:
In this photo you can see the view under the hood. All the wiring and controls were mounted on a sheet of plywood, per Electric Vehicles of America's recommendations. While wood may seem a bit "crude", it is rigid and is a good insulator. This setup minimizes the risk of a short of the high voltage to the vehicle's chassis. Appropriately, the plywood is painted an "electric blue" color.
The large, oblong black box in the center of the photo is an electronic controller that provides pulse-width modulated high voltage to the motor. To the left and front of that is a smaller, square black box which serves to convert the 120 volts DC motor supply power to 12 volts to keep the 12 volt control battery charged. When the truck is plugged in to charge, the 12 volt system is thus recharged as well. Two large contactors electrically disconnect the high voltage supply when the truck is parked. One serves as an interlock that is operated when the "ignition" switch is turned to "on". The other contactor is actuated by a microswitch in the throttle control when the accelerator pedal is pressed slightly. A potentiometer in the throttle control works with the motor controller to regulate the speed of the motor. The throttle control box can be seen in the right-hand side of the picture. The high voltage wiring is the large diameter orange cables seen in the pictures. A small electrically operated vacuum pump supplies the power brake booster, since there is no longer a gas engine to supply this.
Sixteen of the batteries, along with the charger, are stored in the rear bed of the truck; the remaining four are secured just behind the front radiator grille. The "shore power" connector for recharging the truck is installed where the gasoline filler used to be. This can be seen in the pictures at the bottom of the post.
Conceptually, a "plug-in" electric vehicle of this type is very simple.
The original control wiring was done with cheap, insulated slide on connectors bought at a local auto parts store. Over time these connections worked loose and became intermittent. Last Fall, the professor in charge of the electric vehicle project asked me to do whatever repairs were needed to make the vehicle reliable. I made several suggestions on what needed to be done and gave the professor a parts list. Upon his approval I proceeded.
I ended up replacing most of the control wiring, along with the cheap 1/4" crimp-on slide connectors. The original wiring was #18 gauge; I replaced it with #14. The new connectors, bought from McMaster Carr, were the non-insulated crimp type. I crimped each connector to the wire, then soldered it, then used adhesive-lined heat-shrink tube to insulate the connection. I labeled each connector with a P-touch label, then covered that with clear heat-shrink tubing for protection and to keep the labels from falling off. Doing wiring this way is time consuming, but it vastly improves reliability and makes tracing the wiring for repair a snap. For years I have done this on my own vehicles, too. [On my older truck, when it came time to replace the vacuum lines, I used P-touch labels and clear heat-shrink tube on all of the new hoses as I installed them. Now, at a glance, I know which hoses go where without having to consult the manual.]
You can see pictures of the electric truck wiring, batteries, throttle control, and of the motor below.